I believe this may be related to port settings on our routers. But I find it odd that I've had no trouble in the many years playing FFXI and the problem started immediately after the 5/9/2011 update.
I've taken the following steps:
1) Check files (no trouble found)
2) Tested other platforms, problem persists on PC, PS2 and Xbox 360, same characters, same zones getting stuck on the downloading data zone screen
3) Reset router to default settings (Using a Linksys WRT54G wireless router Ver. 6.0)
4) Installed latest firmware
5) Set up wireless network
6) Set up static IP address
7) Enabled port forwarding, opening ports used by FFXI/POL
8) Had ISP check out connection (I use a local Fiber Optic provider)
9) Turn off firewall
Still having the same issues.
If I bypass my router and connect directly to the firber optic line, I am able to zone without trouble on my main into Lower Jeuno. If I use the same device connected through my router, I get the error again.
Unfortunately, I need to use my router I'm not hogging the internet in my house.
Also, after searching the internet on this issue, I have found occasions where other people had this problem after FFXI version updates and some just had to wait it outMost said to enable port forwarding on your router, but this is certainly not resolving the issue for me.